Such portable measuring instruments are already known. These portable devices are particularly employed for detecting, by optical means, the heart rhythm and/or the level of oxygen in a patient's blood. They are found in various forms ranging from clamps intended to be placed on a zone of the human body (typically on the end of a finger, on the earlobe or any other extremity of the human body sufficiently irrigated by blood) to devices worn on the wrist having a similar appearance to a wristwatch.
Within the scope of an application to measurement of the heart rhythm, the optical device is used for generating adequate illumination of a portion of the organic tissue (typically the skin) and includes one or several photoreceptors for detecting the intensity of the light emission produced by the optical device after propagation in the organic tissue. Variations in the blood flow pulsation induce a variation in the absorption of the luminous emission produced by the optical device, the frequency of said absorption variation essentially corresponding to the frequency of the heart pulsations. Detection of the intensity of the light emission after propagation in the organic tissue accompanied by adequate processing of the measurement signal or signals enables one to extract an indication of the heart rhythm. The optical devices commonly used for this type of application are relatively simple and typically consist of LEDs (light emitting diodes) emitting within a determined wavelength range, associated with one or several photoreceptors, typically photodiodes.
In addition to the function of measuring the desired physiological quantity, the portable instruments fitted with optical devices of the aforementioned types are also commonly fitted with means for emitting and/or receiving data. In particular, emission means are typically provided for downloading onto an external terminal data measured and stored in the portable instrument during periods of activity, for example during physical activity or during a health diagnosis. Moreover, reception means can be provided for loading configuration data in the portable instrument, for example limit values for the measured physiological quantity such as minimum and maximum heart rhythm values, between which the user wishes to keep his heart rhythm. The data emitted from the portable instrument or received by the portable instrument may or may not be related to the measured physiological quantity.
The emission and/or the reception of data can commonly be carried out by direct cable link or preferably owing to wireless communication means that may, for example, be of the acoustic, optical, inductive or radio-frequency type.
Patent document Nos. U.S. Pat. No. 4,674,743, EP 0 842 635 and U.S. Pat. No. 5,776,056 disclose various portable instruments provided with an optical device of the aforementioned type for measuring a physiological quantity as well as optical data communication means. These documents however disclose solutions employing distinct optical devices.
As mentioned, other known solutions rely upon communication means of the acoustic, inductive or radio-frequency type. By way of example, documents EP 0 940 119, U.S. Pat. No. 5,810,736, U.S. Pat. No. 5,622,180 or WO 99/41647 and EP 1 101 439 can be cited.
All of the aforementioned prior art solutions, including solutions employing optical communication means, have the drawback of requiring specific additional requirements which influence the manufacturing costs of the portable instrument and inevitably require space in order to be incorporated. These solutions are not, therefore, optimal in terms of compactness and manufacturing costs.
It is thus a general object of the present invention to propose a portable instrument of the aforementioned type, which allows both a reduction in costs and a reduction in the size of the portable instrument with respect to solutions of the prior art.